Piezoelectric ceramic composition

ABSTRACT

A piezoelectric ceramic composition contains a perovskite composition which is represented by (Pba.Rex){Zr b .Ti c , .(Ni 1/3 Nb 2/3 ) d .(Zn 1/3 Nb 2/3 ) e }O 3  (wherein Re represents La and/or Nd, and a-e and x satisfy the following conditions 0.95≦a≦1.05, 0≦x≦0.05, 0.35≦b≦0.45, 0.35≦c≦0.45, 0&lt;d≦0.10, 0.07≦e≦0.20 and b+c+d+e=1) and 0.05-0.3% by mass of an Ag component in terms of oxides relative to the perovskite composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

this application is a divisional of U.S. patent application Ser. No.14/360,275, filed May 22, 2014, and claims the benefits thereof underU.S.C. §121 or §365(c), which is the U.S. National Phase under 35 U.S.C.§371 of International Application PCT/JP2012/080545, filed Nov. 27,2012, which claims priority to Japanese Patent Application No.2011-278228, filed Dec. 20, 2011, the disclosure of each of which isherein incorporated by reference in its entirety. The InternationalApplication was published under PCT Article 21(2) in the language otherthan English.

The applicant(s) herein explicitly rescind(s) and retract(s) any priordisclaimers or disavowals made in any parent, child or relatedprosecution history with regard to any subject matter supported by thepresent application.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a piezoelectric device such as anacoustic element, piezoelectric actuator, etc., particularly suitablefor use in a high-temperature environment, as well as a piezoelectricceramic composition used for such piezoelectric device.

2. Background Art

Piezoelectric ceramic compositions are used as electromechanicalconversion materials for piezoelectric devices such as acousticelements, piezoelectric actuators, etc.

For example, Patent Literature 1 discloses a ferroelectric ceramicconstituted by a perovskite solid solution expressed byPb_(1-(3/2)a)M_(a){(Ni_(1/3)Nb_(2/3))_(1-b)(Zn_(1/3)Nb_(2/3))_(b)}_(x)Ti_(y)Zr_(z)O₃[where M is at least one type of element selected from a group thatincludes La and Nd, and x+y+z=1, a=0.005 to 0.03, b=0.5 to 0.95, x=0.1to 0.4, y=0.3 to 0.5 and z=0.2 to 0.5] and containing 0.3 to 1.0 percentby weight of MnO₂.

Piezoelectric devices are adopting laminated structures in recent yearsfor the purpose of performance improvement, lowering of driving voltage,and so on.

However, the ferroelectric ceramic in Patent Literature 1 involves ahigh sintering temperature of 1130 to 1300° C. and therefore requires alot of thermal energy for sintering. In addition, an Ag alloy with highPt or Pd content must be used as the material for internal electrodes tobe sintered simultaneously with the ferroelectric ceramic, whichpresents a problem of adding to the cost of the piezoelectric device.

In light of the above, piezoelectric ceramic compositions that can besintered at low temperature have been developed to lower the costs ofpiezoelectric devices.

Patent Literature 2 discloses a piezoelectric ceramic compositionconstituted by a perovskite composition expressed byPb_(a){Zr_(b).Ti_(c).(Ni_(1/3)Nb_(2/3))_(d). (Zn_(1/3)Nb_(2/3))_(e)}O₃[where b+c+d+e=1, 1.000≦a≦1.020, 0.26≦b≦0.31, 0.34≦c≦0.40, 0.10≦d≦0.35and 0.07≦e≦0.14] and also by Ag₂O contained in the perovskitecomposition, wherein this Ag₂O is contained by a ratio of 0.005 to 0.03percent by weight, and it is claimed that this piezoelectric ceramiccomposition can be sintered at 900° C. or so.

PRIOR ART LITERATURES Patent Literatures

Patent Literature 1: Japanese Patent Laid-open No. Hei 3-215359

Patent Literature 2: Japanese Patent No. 4202657

SUMMARY OF THE INVENTION Problems to Be Solved by the Invention

However, piezoelectric devices using the piezoelectric ceramiccomposition in Patent Literature 2 have a high coercive electric fieldand thus are difficult to apply for use at high temperature. Their highdielectric constant c also presents a problem in that thesepiezoelectric devices have increased levels of power consumption.

Accordingly, the object of the present invention is to provide apiezoelectric device and piezoelectric ceramic composition suitable foruse in a high-temperature environment.

Means for Solving the Problems

To achieve the aforementioned object, the piezoelectric device proposedby the present invention is a piezoelectric device having apiezoelectric ceramic layer obtained by sintering a piezoelectricceramic composition that contains a perovskite composition and Agcomponent, as well as a conductor layer sandwiching the piezoelectricceramic layer; wherein such piezoelectric device is characterized inthat the piezoelectric ceramic layer has Ag segregated in the voidspresent in the sintered compact of the perovskite composition.

Preferably the perovskite composition contains a zirconate-titanate typeperovskite composition and/or alkali-containing niobate type perovskitecomposition.

Preferably the piezoelectric device proposed by the present invention issuch that the grain size of the Ag segregated in the voids present inthe sintered compact of the perovskite composition is 0.1 to 3 μm in d80diameter.

The

piezoelectric ceramic composition of the piezoelectric device proposedby the present invention contains a zirconate-titanate type perovskitecomposition expressed by Formula (1) below, as well as an Ag component;wherein, preferably the Ag component is contained by 0.05 to 0.3 partsby mass per 100 parts by mass of the zirconate-titanate type perovskitecomposition in terms of oxides:

(Pb_(a).Re_(x))(Zr_(b).Ti_(c).(Ni_(1/3)Nb_(2/3))_(d).(Zn_(1/3)Nb_(2/3))_(e))O₃  (1)

In the formula, Re represents La and/or Nd, and a to e and x meet therespective requirements below:

0.95≦a≦1.05

0≦x≦0.05

0.35≦b≦0.45

0.3≦c≦0.45

0<d≦0.10

0.07≦e≦0.20

b+c+d+=1

The perovskite composition of the piezoelectric device proposed by thepresent invention is an alkali-containing niobate type perovskitecomposition expressed by Formula (2) below; wherein, preferably thepiezoelectric ceramic layer has a Si and K-containing crystalline ornon-crystalline substance present at the grain boundaries or grainboundary triple points of crystal grains constituted by a sinteredcompact of the perovskite composition:

(Li,Na_(m)K_(1-1-m))_(n)(Nb_(1-e)Ta_(o))O_(a)   (2)

In the formula, 1 to o meet the respective requirements below:

0.04<I≦0.1

0≦m≦1

0.95≦n≦1.05

0≦o≦1

The piezoelectric device proposed by the present invention is such that,preferably the conductor layer is formed by Ag, Pd, Pt, Ni, Cu, or anyalloy containing at least one of the foregoing.

Additionally, the piezoelectric ceramic composition proposed by thepresent invention is characterized in that it contains azirconate-titanate type perovskite composition expressed by Formula (1)below, as well as an Ag component; wherein the Ag component is containedby a ratio of 0.05 to 0.3 parts by mass per 100 parts by mass of thezirconate-titanate type perovskite composition in terms of oxides:

(Pb_(a).Re_(x))(Zr_(b).Ti_(c).(Ni_(1/3)Nb_(2/3))_(d).(Zn_(1/3)Nb_(2/3))_(e))O₃   (1)

In the formula, Re represents La and/or Nd, and a to e and x meet therespective requirements below:

0.95≦a≦1.05

0≦x≦0.05

0.35≦b≦0.45

0.35≦c≦0.4 5

0<d≦0.10

0.07≦e≦0.20

b+c+d+e=1

The piezoelectric ceramic composition proposed by the present inventionis such that, preferably the maximum grain size of the Ag component is 3μm or less.

Effects of the Invention

According to the piezoelectric device proposed by the present invention,where the piezoelectric ceramic composition contains a perovskitecomposition and Ag component, the sintering temperature of thepiezoelectric ceramic composition is low and therefore Ag or any Agalloy with high Ag content can be used for the conductor layer. Alsobecause the piezoelectric ceramic layer has Ag segregated in the voidspresent in the sintered compact of the perovskite composition, thecoercive electric field increases and the resulting piezoelectric devicebecomes suitable for use in a high-temperature environment. Furthermore,even when Ag or any Ag alloy is used for the conductor layer, Ag in theconductor layer will diffuse to the piezoelectric ceramic layer toprevent conductor layer deficiency, which in turn suppresses lowering ofcharacteristics.

Moreover, the resulting piezoelectric device will have goodpiezoelectric characteristics so long as the grain size of Ag segregatedin the voids present in the sintered compact of the perovskitecomposition is 0.1 to 3 μm in d80 diameter.

In addition, the piezoelectric ceramic composition containing azirconate-titanate type perovskite composition expressed by Formula (1)above, as well as an Ag component, wherein the Ag component is containedby 0.05 to 0.3 parts by mass per 100 parts by mass of the perovskitecomposition in terms of oxides, forms a piezoelectric ceramic layer ofhigh Curie temperature Tc, high coercive electric field, and lowdielectric constant and can be sintered at low temperatures of 900° C.and below, and thus allows Ag or any Ag alloy with low Ag content to beused as the conductor metal material. As a result, a piezoelectricdevice of low power consumption suitable for use in a high-temperatureenvironment can be manufactured at low cost.

In addition, the piezoelectric ceramic layer characterized by a Si andK-containing crystalline or non-crystalline substance present at thegrain boundaries or grain boundary triple points of crystal grainsconstituted by a sintered compact of the alkali-containing niobate typeperovskite composition expressed by Formula (2) above, provides apiezoelectric device of low power consumption suitable for use in ahigh-temperature environment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic section view of the piezoelectric device proposedby the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS Mode for Carrying Out the PresentInvention

As shown in FIG. 1, the piezoelectric device proposed by the presentinvention has a piezoelectric ceramic layer where Ag is segregated inthe voids present in the sintered compact of the perovskite composition,as well as a conductor layer sandwiching the piezoelectric ceramiclayer.

Segregating Ag in the voids present in the sintered compact of theperovskite composition makes Ag an oxygen supply source duringsintering, which in turn has the effect of lowering the liquid-phasegeneration temperature. This way, the oxygen and Pb defect of the basebody is suppressed and the material's thermodynamic stability increases,and as a result, the coercive electric field increases and the resultingpiezoelectric device becomes suitable for use in a high-temperatureenvironment. Furthermore, segregating Ag in the voids present in thesintered compact of the perovskite composition allows Ag in theconductor layer to diffuse to the piezoelectric ceramic layer, even whenAg or any Ag alloy is used for the conductor layer, and consequentlyconductor layer deficiency is prevented and property degradation can besuppressed.

Whether or not Ag is segregated in the voids present in the sinteredcompact of the perovskite composition can be observed using a TEM(transmission electron microscope) or SEM (scanning electronmicroscope), and the segregated Ag can be quantified by measuring itssize distribution. In addition, whether the segregated Ag is metal Ag,not an oxide, can be checked by means of composition analysis based oncharacteristic X-rays.

Under the present invention, the piezoelectric ceramic layer is suchthat, preferably the grain size of the Ag segregated in the voidspresent in the sintered compact of the perovskite composition is 0.1 to3 μm in d80 diameter. The resulting piezoelectric device will have goodpiezoelectric characteristics so long as the grain size of segregated Agis within the aforementioned range. If the d80 diameter exceeds 3 μm ata given point, that point tends to become an origin of lower breakdownvoltage and, because the number of Ag grains between the piezoelectricceramic layers decreases, the pressure resistance longevity traits tendto drop. If the d80 diameter is less than 0.1 μm, on the other hand, Agbecomes uniformly diffused in the sintered compact and consequently thepiezoelectric characteristics, etc., tend to deteriorate.

Under the present invention, segregated Ag was observed using a TEMimage. The grain size of Ag was obtained by measuring the grain sizes of200 Ag grains randomly selected on a TEM image by means of binarizationand measurement of the lengths of parts determined as Ag, and then usingthe results to obtain the cumulative volume diameter and then the d80diameter.

For the piezoelectric ceramic composition used to form the piezoelectricceramic layer, one containing a perovskite composition and Ag componentis used.

Preferably the perovskite composition is a zirconate-titanate typeperovskite composition and/or alkali-containing niobate type perovskitecomposition.

For the zirconate-titanate type perovskite composition, one based on thecompositional structure expressed by Formula (1) below is usedpreferably:

(Pb_(a).Re_(x))(Zr_(b).Ti_(c).(Ni_(1/3)Nb_(2/3))_(d).(Zn_(1/3)Nb_(2/3))_(e))O₃  (1)

In Formula (1), Re represents La and/or Nd.

In Formula (1), a is qualified by 0.95≦a≦1.05, where 1.00≦a≦1.02 ispreferred. If a<0.95, excellent piezoelectric characteristics will stillbe obtained, but low-temperature sintering becomes impossible even whenAg is added; whereas, a>1.05 will cause the secondary Pb phase depositsen masse and the piezoelectric characteristics will drop to anon-practical level. By adjusting a within the aforementioned range, apiezoelectric ceramic composition of small ceramic grain size can beobtained that exhibits good piezoelectric characteristics based onsintering at 900° C.

In Formula (1), x is qualified by 0≦x≦0.05, where 0.003≦x≦0.007 ispreferred. In other words, the perovskite composition in Formula (1) mayhave its Pb partially substituted by La and/or Nd. Partiallysubstituting Pb by La and/or Nd increases the piezoelectric constant.The Curie temperature Tc drops if x>0.05. By adjusting x within theaforementioned range, the piezoelectric constant can be raised whilekeeping a high Curie temperature Tc of 300° C. or above.

Furthermore, adjusting a+x to the range of 1.00≦a+x≦1.02 is preferred.That is because, with the perovskite of Formula (1), the characteristicscan also be maintained by adjusting the AB ratio of an ABO₃ typeperovskite within a range of 1.00 to 1.02.

In Formula (1), b is qualified by 0.35≦b≦0.45, where 0.38≦b≦0.42 ispreferred. The Curie temperature Tc drops if b<0.35, whereas thepiezoelectric constant drops if b>0.45. By adjusting b within theaforementioned range, the piezoelectric constant can be raised whilekeeping a high Curie temperature Tc of 300° C. or above.

In Formula (1), c is qualified by 0.35≦c≦0.45, where 0.38≦c≦0.42 ispreferred. The Curie temperature Tc drops ifc<0.35, whereas thepiezoelectric constant drops if c>0.45. By adjusting c within theaforementioned range, the piezoelectric constant can be raised whilekeeping a high Curie temperature Tc of 300° C. or above.

In Formula (1), d is qualified by 0<d≦0.10, where 0.3≦d≦0.7 ispreferred. The Curie temperature Tc remains high but the piezoelectricconstant drops if d=0, whereas the Curie temperature Tc drops if d>0.10.By adjusting d within the aforementioned range, the piezoelectricconstant can be raised while keeping a high Curie temperature Tc of 300°C. or above.

In Formula (1), e is qualified by 0.07≦e≦0.20, where 0.13≦e≦0.17 ispreferred. If e<0.07, the base body undergoes significant grain growthand can no longer maintain a fine structure, thus making low-temperaturesintering impossible; whereas, if e>0.20, the piezoelectric constantdrops. By adjusting e within the aforementioned range, the feasibilityof low-temperature sintering, and the piezoelectric constant, can bemaintained.

In Formula (1), b+c+d+e=1.

For the alkali-containing niobate type perovskite composition, one basedon the compositional structure expressed by Formula (2) below is usedpreferably. A piezoelectric device having a piezoelectric ceramic layerin which a Si and K-containing crystalline or non-crystalline substanceis present at the grain boundaries or grain boundary triple points ofcrystal grains constituted by a sintered compact of an alkali-containingniobate type perovskite composition expressed by Formula (2), has lowpower consumption and is suitable for use in a high-temperatureenvironment:

(Li,Na_(m)K_(1-1-m))_(n)(Nb_(1-e)Ta_(o))O_(a)   (2)

In Formula (2), preferably 1 is in the range of 0.04<1≦0.1. If 1≦0.04 or1>0.1, the piezoelectric constant at room temperature tends to drop.

In Formula (2), preferably m is in the range of 0≦m≦1. If m>1, asecondary phase is formed and the piezoelectric constant tends to drop.

In Formula (2), preferably n is in the range of 0.95≦n≦1.05. If n<0.95or n>1.05, a secondary phase is formed and the piezoelectric constanttends to drop.

In Formula (2), preferably o is in the range of 0≦o≦1. If o>1, asecondary phase is formed and the piezoelectric constant tends to drop.

For the piezoelectric ceramic composition under the present invention,one containing a zirconate-titanate type perovskite compositionexpressed by Formula (1), as well as an Ag component corresponding to0.05 to 0.3 parts by mass per 100 parts by mass of thezirconate-titanate perovskite composition in terms of oxides, is used.This piezoelectric ceramic composition can be sintered at lowtemperatures of 900° C. and below, and allows for manufacturing of apiezoelectric device by using Ag or any Ag alloy with high Ag content asthe conductor layer material. In addition, the piezoelectric ceramiclayer obtained by sintering this piezoelectric ceramic composition has ahigh Curie temperature Tc of 300° C. or above, high coercive electricfield of 0.8 kV/mm or more even at 120° C., and low dielectric constantc in a range of 1800 to 2200, and therefore the resulting piezoelectricdevice has low power consumption and becomes more suitable for use in ahigh-temperature environment. It should be noted that, under the presentinvention, the Curie temperature Tc, coercive electric field, anddielectric constant c represent values measured according to the methodsdescribed later in “Examples.”

Examples of the Ag component contained in the piezoelectric ceramiccomposition include an oxide of Ag (Ag₂O) and carbonate of Ag (Ag₂CO₃),among others.

Preferably the maximum grain size of the Ag component is 3 μm or less.When the maximum grain size of the Ag component is 3 μm or less, Agsegregates easily in the voids present in the sintered compact of theperovskite composition. If it exceeds 3 μm, on the other hand, the Agcomponent deposits on the surface of the sintered compact and forms asecondary phase of Ag component, potentially causing the productlongevity traits of the piezoelectric device to drop. There is no limitto how the maximum grain size of the Ag component is adjusted to 3 μm orless, and a method involving sifting of powder or method based onfiltering of slurry can be used, for example.

Under the present invention, the grain size of the Ag component wasmeasured using a TEM, with the largest of 200 randomly selected grainstaken as the maximum grain size.

The Ag component is contained preferably by 0.05 to 0.3 parts by mass,or more preferably by 0.07 to 0.15 parts by mass, per 100 parts by massof the perovskite composition in terms of oxides. If the Ag component iscontained by less than 0.05 parts by mass, the tendency is thatsintering at low temperatures becomes difficult, the bulk density (truedensity of the sintered compact) at 900° C. becomes low, and themoisture resistance characteristics deteriorate; whereas, if the Agcomponent is contained by more than 0.3 parts by mass, the Ag componentmay deposit on the surface of the sintered compact and form a secondaryphase of Ag component, thereby causing the product longevity traits ofthe piezoelectric device to drop. So long as the Ag component iscontained by an amount within the aforementioned range, a piezoelectricceramic layer in which Ag is segregated in the voids present in thesintered compact of the perovskite composition can be formed with ease.

Under the present invention, the piezoelectric ceramic composition canalso contain a Mn component. When a Mn component is contained, theobtained piezoelectric ceramic layer is hardened, the Q value increases,and the power consumption of the piezoelectric device can be reducedfurther.

Preferably the Mn component is contained by 0 to 1 percent by mass per100 parts by mass of the perovskite composition in terms of oxides. Alsounder the present invention, the piezoelectric ceramic composition canalso contain a Co component. When a Co component is contained, thepiezoelectric characteristics and dielectric characteristics can befinely adjusted to desired characteristics. Preferably the Co componentis contained by 0 to 1 percent by mass per 100 parts by mass of theperovskite composition in terms of oxides.

Under the present invention, preferably the grain size of the sinteredcompact of the perovskite composition is 3 μm or less. This way, thepressure resistance longevity traits can be improved.

The piezoelectric ceramic composition containing a zirconate-titanatetype perovskite composition expressed by Formula (1) is obtained bymixing oxides, carbonates, etc., of Pb, La, Zr, Ti, Ni, Nb, and/or Zn tothe stoichiometric ratios of a zirconate-titanate type perovskitecomposition expressed by Formula (1) and then agitating the mixture inwater or other wet environment, followed by drying and sintering for 2to 4 hours at 820 to 850° C. in atmosphere. This way, the metalcomponents undergo solid solution reaction against one another to form azirconate-titanate type perovskite composition expressed by Formula (1)above. The formed perovskite composition is wet or dry-crushed and thenan Ag component is added, preferably by 0.05 to 0.3 parts by mass per100 parts by mass of the perovskite composition, after which the mixtureis dried. The Ag component can be added together with other materialswhen the perovskite composition is formed, but preferably it is addedafter the perovskite composition has been formed. By adding the Agcomponent after the perovskite composition has been formed, Agsegregates more easily in the voids present in the sintered compact ofthe perovskite composition.

Also, the piezoelectric ceramic composition containing analkali-containing niobate type perovskite composition expressed byFormula (2) is obtained by mixing oxides, carbonates, etc., of Li, Na,K, Nb, and/or Ta to the stoichiometric ratios of an alkali-containingniobate type perovskite composition expressed by Formula (2) and thensintering in the same manner described above, so that the metalcomponents undergo solid solution reaction against one another to forman alkali-containing niobate type perovskite composition expressed byFormula (2) above. The formed perovskite composition is wet ordry-crushed and then an Ag component is added, preferably by 0.05 to 0.3parts by mass per 100 parts by mass of the perovskite composition, afterwhich the mixture is dried.

With the piezoelectric device proposed by the present invention, thematerial to constitute the conductor layer is not limited in any way. Alow-resistance material is preferred, and Ag, Pd, Pt, Ni, Cu, or anyalloy containing at least one of the foregoing is more preferred. Forthe alloy, an Ag—Pd alloy or Ag—Pt alloy is preferred.

The piezoelectric device proposed by the present invention has low powerconsumption and is suitable for use in a high-temperature environment,and for example, it can be used particularly favorably in applicationssuch as onboard speakers and other acoustic elements, piezoelectricactuators, and supersonic motors.

The aforementioned piezoelectric device can be manufactured, forexample, using the method described below.

Binder, solvent, plasticizer, etc., are added to a piezoelectric ceramiccomposition containing a perovskite composition and Ag component toprepare a slurry, which is then formed to a thin film using the doctorblade method, etc., to manufacture a green sheet. Examples of binderinclude polyvinyl butyral resin and methacrylate resin, among others.Examples of plasticizer include dibutyl phthalate and dioctyl phthalate,among others. Examples of solvent include toluene and methyl ethylketone, among others.

Next, a conductor paste containing Ag, Ag—Pd alloy, Ag—Pt alloy, orother conductor metal is printed onto the obtained green sheet using thescreen printing method, etc., to form an unsintered internal conductorlayer of a specified pattern.

Next, multiple green sheets, each having an unsintered internalconductor layer formed on it, are stacked on top of one another and thenpressure-bonded to manufacture an unsintered laminate.

Next, the unsintered laminate is put through a binder removal process,and then cut to a specified shape so that the unsintered internalconductor layer is exposed at the ends of the unsintered laminate.Thereafter, the end faces of the unsintered laminate are printed with aconductor paste containing a conductor metal, using the screen printingmethod or other method, to form unsintered external electrode layers.

Next, the unsintered laminate on which unsintered base metal has beenformed is sintered for 2 to 3 hours at 850 to 900° C. in an oxygenambience. This way, the aforementioned piezoelectric device proposed bythe present invention, where piezoelectric ceramic layers are sandwichedby conductor layers, can be manufactured.

EXAMPLES

PbO, La₂O₃, ZrO₂, TiO₂, NiO, ZnO, Nb₂O₅ and Ag₂O were prepared asmaterial powders and the material powders were sifted to adjust theirmaximum grain size to 3 μm or less, respectively. Thereafter, the siftedmaterial powders of perovskite composition were weighed to each set ofratios shown in Table 1 and put in a pot mill together with zirconiabeads and ion exchange water and then wet-mixed for 15 hours, afterwhich the obtained suspension liquid was transferred to a vat that wasthen put in a dryer and dried at 150° C.

TABLE 1 Piezoelectric ceramic composition Amount of Ag₂O added*Constituents of perovskite composition (part a x b c d e by mass)Sample 1.00 0.005 0.40 0.40 0.05 0.15 0.10 1A (Re = La) Sample 1.000.005 0.40 0.40 0.05 0 15 0.10 1B (Re = Nd) Sample 2 1.00 0 0.26 0.400.26 0.08 0.01 Sample 3 1.00 0.005 0.40 0.40 0.05 0.15 0.00 (Re = La)Sample 4 1.00 0.005 0.40 0.40 0.05 0.15 0.40 (Re = La) Sample 5 1.06 00.40 0.40 0.05 0.15 0.10 Sample 6 0.94 0 0.40 0.40 0.05 0.15 0.10 Sample7 1.00 0.6 0.40 0.40 0.05 0.15 0.10 (Re = La) Sample 8 1.00 0 0.50 0.380.05 0.07 0.10 Sample 9 1.00 0 0.38 0.50 0.05 0.07 0.10 Sample 10 1.00 00.37 0.37 0.15 0.13 0.10 Sample 11 1.00 0 0.40 0.40 0 0.20 0.10 Sample12 1.00 0 0.37 0.37 0.05 0.26 0.10 Sample 13 1.00 0 0.45 0.45 0.07 0.030.10*(Pb_(a)•Re_(x)){Zr_(b)•Ti_(c)•(Ni_(1/3)Nb_(2/3))_(d)•(Zn_(1/3)Nb_(2/3))_(e)}O₃

Next, the dried mixture was sintered for 2 hours at 850° C. inatmosphere using an electric furnace. The metal oxides in the mixtureunderwent solid solution reaction against one another during sinteringand a perovskite composition was formed.

Next, this perovskite composition and Ag₂O that had been weighed to eachratio shown in Table 1 were put in a pot mill together with zirconiabeads and ion exchange water and then wet-crushed for 15 hours, afterwhich the obtained suspension liquid was transferred to a vat that wasthen put in a dryer and dried at 150° C., to obtain a piezoelectricceramic composition.

Next, each piezoelectric ceramic composition was mixed with a smallamount of polyvinyl butyral and the mixture was compression-molded witha press machine at a pressure of 1.5 MPa, to obtain a disc-shaped sampleof 8 mm in diameter and 0.5 mm in thickness.

Next, this sample was put in an electric furnace and sintered for 2hours at 900 to 1050° C. in atmosphere, after which the sample was takenout of the electric furnace and printed with a fritless Ag paste on bothsides, and then baked at 700° C. in atmosphere so as to use the bakedpaste as external electrodes.

This disc-shaped sample with external electrodes installed on it wasmeasured for temperature dependence of dielectric constant c attemperatures from 40 to 400° C., to obtain the Curie temperature Tc.Also, a TF analyzer was used to measure the hysteresis of each sampleunder the conditions of 25° C., 1 Hz, and 3 kV/mm, to calculate thecoercive electric field. Next, voltage of 1.5 kV/mm was applied to thissample with external electrodes for 15 minutes at 150° C., to polarizethe sample. Next, the piezoelectric constant Kr of this polarized samplewas measured, the result of which is shown in Table 1. The piezoelectricconstant Kr was calculated by measuring the impedance according to theapplicable standard of the Japan Electronics and Information TechnologyIndustries Association (JEITA EM-4501). The result is shown in Table 2.

TABLE 2 Sintering Curie Coercive Piezoelectric temperature temperatureDielectric electric field constant (° C.) Tc (° C.) constant ε (kV/mm)Kr (%) Other Sample 1A 900 310 2000 1.2 70 Ag is segregated in the voidspresent in the sintered compact of the perovskite composition. Sample 1B900 310 2010 1.2 71 Same as above. Sample 2 900 230 3460 0.93 65 Ag isdispersed almost uniformly in the sintered compact of the perovskitecomposition. Sample 3 1050 310 2100 1.2 70 Could not be sintered at 900°C. Sample 4 900 310 2200 1.2 55 Ag is segregated in the voids present inthe sintered compact of the perovskite composition, but a secondary Agphase is formed in the surface layer. Sample 5 900 — — — — Measurementwas not possible due to depositing of a secondary Pb phase. Sample 61000 305 2340 1.2 58 Could not be sintered at 900° C. Sample 7 900 2802900 0.98 64 The Tc dropped and the coercive electric field decreased.Sample 8 900 315 1950 1.2 57 The piezoelectric constant dropped. Sample9 900 317 1920 1.3 55 The piezoelectric constant dropped. Sample 10 900283 2500 0.97 64 The Tc dropped and the coercive electric fielddecreased. Sample 11 900 317 2100 1.2 53 The piezoelectric constantdropped. Sample 12 900 310 2100 1.2 54 The piezoelectric constantdropped. Sample 13 900 319 2030 1.2 56 The piezoelectric constantdropped.

Additionally, the piezoelectric ceramic compositions of Samples 1A, 1Band 2 were used to form green sheets using the doctor blade method, andthe obtained green sheets were printed with an Ag paste using the screenprinting method, to form unsintered internal conductor layers.

Next, 11 green sheets on which unsintered internal conductor layers wereformed were stacked on top of one another, after which cover sheets,each produced by stacking to a specified thickness a number of identicalsheets with no paste printed on them, were placed at the top and bottomto sandwich the green sheets, and then all sheets were pressure-bondedto manufacture an unsintered laminate.

Next, this unsintered laminate was put in an electric furnace andsintered for 2 hours at 900° C. in atmosphere, to manufacture alaminate. A TEM image of the obtained laminate was taken to check if Agwas segregated in the voids present in the sintered compact of theperovskite composition. In addition, EDS (energy-dispersive X-rayspectroscopy) was used to check whether oxygen was detected or not.

The piezoelectric device of Sample 1 had Ag segregated in the voidspresent in the sintered compact of the perovskite composition. The grainsize of this segregated Ag was 2.1 μm in d80 diameter. Moreover, EDS didnot detect oxygen in the segregated Ag, and the segregated Ag was metalAg, not an oxide. Then, as shown in Table 1, this piezoelectric devicehad a high Curie temperature Tc and high coercive electric field, couldbe driven at high temperatures of 105° C. and above, and was suitablefor use at high temperatures. In addition, its dielectric constant c waslow and power consumption was low. Furthermore, the piezoelectricceramic composition could be sintered at 900° C. or below.

Similar results were also obtained from Sample 1B whose Re was Nd.Samples 1A and 1B are considered piezoelectric ceramic compositionsconforming to the present invention.

On the other hand, the piezoelectric device of Sample 2 had Ag dispersedalmost uniformly relative to the piezoelectric ceramic layer andsegregation of Ag could not be confirmed in the voids. In addition, itslow Curie temperature Tc and low coercive electric field made thispiezoelectric device unsuitable for use at high temperatures of 105° C.and above. Furthermore, the piezoelectric device also had a highdielectric constant c and high power consumption.

Additionally, the piezoelectric device of Sample 3 that used apiezoelectric ceramic composition containing no Ag component required asintering temperature of 1100° C. or above, and could not be sinteredsimultaneously with Ag or any Ag alloy with high Ag content. Also, theneed for high sintering temperature required more sintering energy andadded to the manufacturing cost.

Additionally, Sample 4 that used a piezoelectric ceramic compositioncontaining more Ag component than the preferable range specified underthe present invention had Ag deposited on the surface of thepiezoelectric ceramic layer, which made the product prone to shorterlongevity traits.

Additionally, Sample 5 whose Pb was adjusted to a>1.05 could not beevaluated for characteristics due to depositing of a secondary Pb phase.

Additionally, Sample 6 whose Pb was adjusted to a<0.95 could not besintered at low temperature.

Additionally, Sample 7 whose Re was adjusted to x>0.05 exhibited a lowerTc and low coercive electric field.

Additionally, Sample 8 whose Zr was adjusted to b>0.45 exhibited a lowerpiezoelectric constant.

Additionally, Sample 9 whose Ti was adjusted to c>0.45 exhibited a lowerpiezoelectric constant.

Additionally, Sample 10 whose (Ni_(1/3)Nb_(2/3)) was adjusted to d>0.10exhibited a lower Tc and low coercive electric field.

Additionally, Sample 11 whose (Ni_(1/3)Nb_(2/3)) was adjusted to d=0exhibited a lower piezoelectric constant.

Additionally, Sample 12 whose (Zn_(1/3)Nb_(2/3)) was adjusted to e>0.20exhibited a lower piezoelectric constant.

Additionally, Sample 13 whose (Zn_(1/3)Nb_(2/3)) was adjusted to e<0.07exhibited a lower piezoelectric constant.

What is claimed is:
 1. A piezoelectric ceramic composition containing azirconate-titanate type perovskite composition expressed by Formula (1)below, as well as an Ag component, wherein the Ag component is containedby 0.05 to 0.3 parts by mass per 100 parts by mass of thezirconate-titanate type perovskite composition in terms of oxides:(Pb_(a).Re_(x))(Zr_(b).Ti_(c).(Ni_(1/3)Nb_(2/3))_(d).(Zn_(1/3)Nb_(2/3))_(e))O₃  (1) wherein Re represents La and/or Nd, and a to e and x meet therespective requirements below:0.95≦a≦1.050≦x≦0.050.35≦b≦0.450.35≦c≦0.450<d≦0.100.07≦e≦0.20b+c+d+e=1
 2. A piezoelectric ceramic composition according to claim 1,wherein a maximum grain size of the Ag component is 3 μm or less.
 3. Apiezoelectric ceramic composition according to claim 1, which issintered wherein Ag is segregated in voids present in a sintered body ofthe perovskite composition.